Safety device for motor vehicles

ABSTRACT

A safety device for motor vehicles includes an impact detection system and a triggering device for triggering a braking operation as a function of a signal of the impact detection system characterized in that the triggering device is designed for the purpose of triggering the braking operation when the impact detection system indicates the beginning of an impact.

FIELD OF THE INVENTION

The present invention relates to a safety device for motor vehiclesincluding an impact detection system and a triggering device fortriggering a braking operation as a function of a signal of the impactdetection system.

BACKGROUND INFORMATION

A safety device of this type is in German Published Patent ApplicationNo. 199 12 301 in which the impact detection system is formed byacceleration sensors which may simultaneously be used for activating anairbag system. If, in a collision with another vehicle, the accelerationmeasured by the acceleration sensor exceeds a certain threshold valueand subsequently, toward the end of the collision, drops again below acertain threshold value, the vehicle brake is automatically activatedafter the drop below the last-mentioned threshold value. The intent isto minimize collision damage caused by an impact on the rear end of thevehicle in particular. The vehicle brake is still deactivated during theactual impact occurrence so that as large a part of the impact energy aspossible is converted into kinetic energy, thereby making less energyavailable for the deformation of the host vehicle. Due to the automaticbraking of the vehicle after impact, the danger is minimized ofsubsequent damage which may occur due to the fact that the host vehicleis propelled forward by the impact on the rear end and then in turn hitsa vehicle in front.

On the other hand, for improving the safety and driving comfort,distance warning systems and distance control systems have beendeveloped which have a position-finding system, in the form of a radarsensor, for example, which makes it possible to locate objects in frontof the host vehicle and to measure their distances and relative speeds.If it turns out that the safety distance to a preceding vehicle is notsufficient then a warning signal is automatically output or the systemautomatically intervenes in the longitudinal guidance of the vehicle toregulate the distance to the preceding vehicle.

Automatic emergency braking systems have also been developed based onthis technology. For example, German Published Patent Application No. 3637 165 describes a system which, based on the positioning data of theradar sensor, automatically detects a situation in which a collision ispresumably no longer avoidable and which calculates the likely time ofcollision and initiates countermeasures on this basis for reducing thecollision damage. In the first step, only a warning indication is outputto the driver. If the driver does not respond, a braking operation withmoderate braking force is automatically initiated in a second step. Ifthis is not sufficient to prevent the collision, then finally emergencybraking with maximum braking force is automatically initiated. However,such emergency braking systems failed to become accepted in practice. Aconsiderable disadvantage is the fact that the previously availablesensor systems do not allow a reliable estimate of the traffic situationso that erroneous triggering may occur which in turn presents aconsiderable accident risk.

In view of this problem, German Published Patent Application No. 101 18707 describes a system which does not automatically initiate anemergency braking operation when a collision risk is detected, butrather prepares the braking system for imminent emergency braking, e.g.,by pre-loading the brake cylinders (pre-fill), so that, when the driverhimself initiates emergency braking, the braking action may be deployedmore quickly. However, avoiding the collision or alleviating collisiondamage is only possible in this system if the driver actively intervenesin the action.

SUMMARY

Example embodiments of the present invention make it possible toalleviate collision damage by automatically triggering emergency brakingwith substantially reduced risk of erroneous triggering.

According to example embodiments of the present invention, this isachieved in a system of the type mentioned at the outset in thatemergency braking is automatically triggered at the very moment at whichthe impact detection system detects the start of an impact.

However, the collision may no longer be avoided using this system, butactivating the brake during the collision (in-crash-brake) makes itpossible that part of the kinetic energy of the host vehicle is used updue to the braking operation. In this way, the extent of damage to thevehicles involved in the collision is reduced.

Modern vehicles are constructed in such a way that, in the event of animpact, a large part of the impact energy is used up by deformation of aso-called crumple zone in the front part of the vehicle body, while therelatively ruggedly designed passenger compartment remains undamaged asmuch as possible. The safety device according to example embodiments ofthe present invention also causes a virtual extension of the crumplezone, thereby reducing the risk of the passenger compartment being tooheavily deformed so that injuries to the vehicle occupants occur. Sinceemergency braking is automatically triggered without involvement of thedriver, the safety device is also effective when the driver, as a resultof the collision, slips from the brake pedal or is no longer able tocontinue the braking operation due to the sustained collision damage.Since the brake remains active even after the collision, it is ensuredthat the vehicle is brought to a standstill at once after the collision.This reduces the risk of further damage because of the vehicle startingto skid and/or colliding with other obstacles. This effect isparticularly advantageous if the vehicle is additionally equipped withan ABS system or an electronic stability system.

Example embodiments of the present invention are particularlyadvantageous in combination with an airbag system which is part of thesafety standard in today's motor vehicles anyway and which absorbs themotion of the vehicle occupants relative to the vehicle (which isadditionally decelerated by emergency braking according to exampleembodiments of the present invention).

If the vehicle is equipped with an airbag system, the impact detectionsystem is conveniently formed by the impact or acceleration sensorsassociated with the airbag system.

In an example embodiment, the safety device includes additionally aposition-finding system and a collision prediction device which predictsan impending collision based on the position data and the travel data ofthe host vehicle. The safety device may be designed in such a way thatthe emergency braking operation is automatically triggered only when thecollision prediction device indicates an imminent collision and then theimpact detection system indicates the beginning of the collision.

Impact detection systems associated with customary airbag systemsgenerally have a relatively high triggering threshold so that erroneoustriggering of the airbag system is avoided.

According to an appropriate refinement of example embodiments of thepresent invention, the safety device is configured in such a way thatthe triggering threshold of the impact detection system is reduced assoon as the collision prediction system indicates an imminent collision.This applies primarily for the triggering threshold which determinestriggering of the emergency braking operation; however, it may also beappropriate to reduce the threshold for triggering the airbag system sothat the airbags deploy their protection effect earlier. The latter isparticularly advantageous in the event of an impact on relatively softobstacles, e.g., the tires of a heavy towing vehicle, since in such animpact the regular triggering threshold of customary airbag systems isfrequently not reached.

Example embodiments of the present invention may also appropriately becombined with an emergency braking system which aims at triggering theemergency braking operation as early as possible in order still to avertthe collision if possible. In such a system, the collision predictiondevice generates a multi-valued signal based on the data of theposition-finding system and the travel data of the host vehicle, themulti-valued signal being a measure for the collision probability andthe emergency braking operation being triggered as soon as the collisionprobability exceeds a certain threshold value. In view of the alreadymentioned risk which emanates from an erroneous triggering of emergencybraking, the threshold value must be selected to be relatively high.Example embodiments of the present invention make it possible that, atleast at the instant of the collision, the emergency braking operationis also initiated when the collision probability does not reach thethreshold value. Therefore, this is advantageous because typically usedposition-finding systems, e.g., radar sensors, may carry out distancemeasurements only until the distance of the obstacle is still greaterthan a certain mean value so that shortly prior to the collision, whenthe distance to the obstacle becomes very small, a reliable calculationof the collision probability is no longer possible.

Exemplary embodiments of the present invention are illustrated in thedrawings and explained in greater detail in the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a safety device according to an exampleembodiment of the present invention;

FIGS. 2 and 3 show diagrams for explaining the mode of action of thesafety device in different situations;

FIG. 4 shows a diagram for explaining the mode of action of a safetydevice according to an exemplary embodiment, and

FIG. 5 shows a flow chart for illustrating the mode of operation of thesafety device.

DETAILED DESCRIPTION

The safety device shown in FIG. 1 includes an electronic data processingsystem 10 which records data of a position-finding system 12, of aspeedometer 14, and of an impact detection system 16. Position-findingsystem 12 is formed by a radar sensor, for example, which locatesobjects, in particular preceding vehicles, in front of the (host)vehicle equipped with the safety device and measures their distances,relative speeds, and azimuth angle. Speedometer 14 measures speed V ofthe host vehicle. Impact detection system 16 is formed, for example, byone or multiple acceleration sensor(s) (inertia sensors) whichmeasure(s) acceleration a of the host vehicle and is/are used, amongother things, to activate an airbag system 18 in the event of acollision.

Data processing system 10 is preferably part of an ACC system (adaptivecruise control) and is used for regulating the speed of the host vehicleand/or, based on the data of position-finding system 12, the distance toa directly preceding vehicle and which, for this purpose, intervenes inthe vehicle's drive system and braking system 20. A man/machineinterface 22 enables the ACC system to transmit information to thedriver in the form of acoustic warning signals, among other things. Forexecuting the different regulation and control functions, the ACC systemhas different function modules which may be designed as specializedhardware or as software modules. These modules include a collisionprediction device 24 and a triggering device 26 which may trigger anemergency braking operation by outputting a braking command B to brakingsystem 20. Collision prediction device 24 evaluates the trafficsituation based on location data of potential obstacles supplied byposition-finding system 12 and based on the travel data of the hostvehicle, in particular based on speed V. Based on the distance data andazimuth angle data, the located objects which are situated in theanticipated travel corridor of the host vehicle are identified. Forestimating this travel corridor, collision prediction device 24 may, ifneeded, record data of additional sensors (not shown), e.g., a yaw ratesensor or a steering angle sensor. Based on the measured distances andrelative speeds of the objects in the travel corridor and based on speedV of the host vehicle, collision prediction device 24 calculates foreach object the deceleration of the host vehicle which would benecessary to avoid a collision with the respective object. If the actualvalue of this deceleration is greater than a plausible value for theactually possible deceleration of the host vehicle, then collisionprediction device 24 decides that a collision is imminent and transmitsa collision signal K to triggering device 26.

Since the data evaluated by collision prediction device 24 may beaffected by more or less significant uncertainties depending on thetraffic situation, collision signal K may optionally also be amulti-valued signal which indicates a certain collision probability P.When triggering device 26 receives collision signal K or when thecollision probability is above a certain threshold value, the triggeringdevice initially induces the output of a warning signal to the drivervia man/machine interface 22. Optionally, it may simultaneously output aprefill signal PF to the braking system 20 to pre-load the brakecylinder in such a way that the brake responds more quickly in the eventof an emergency braking operation to be expected which may be triggeredby the driver or also automatically by the safety device.

In addition, triggering device 26 evaluates acceleration a of the hostvehicle measured by impact detection device 16. If there is a certaincollision probability and acceleration a exceeds a certain thresholdvalue which indicates an incipient collision with an obstacle,triggering device 26 outputs an emergency braking command B to brakingsystem 20 to automatically initiate emergency braking of the vehicle.These procedures shall be illustrated in greater detail based on FIGS. 2and 3. In FIG. 2, curve 28 indicates negative acceleration (−a) measuredby impact detection system 16, i.e., the deceleration of the vehicle asa function of time t. This deceleration is compared with a lowerthreshold value Sa1 and an upper threshold value Sa2. As long as thereis no collision probability, higher threshold value Sa2 applies. Atpoint in time t1, collision prediction device 24 detects an imminentcollision and outputs collision signal K. This causes triggering device26 to reduce the threshold value to Sa1. At the same time, prefillsignal PF is output to braking system 20 and the warning signal isoutput to the driver. At point in time t2, the front bumper of thevehicle hits an obstacle so that the vehicle deceleration increasescorresponding to curve 28. At point in time t3, the deceleration exceedsthreshold value Sa1 and triggering device 26 outputs braking command Bso that the vehicle is now slowed down with maximum braking force. Thefurther course of curve 28 represents the vehicle deceleration duringthe collision process, i.e., during the deformation of the vehicle'scrumple zone. Since the vehicle brake is effective with maximum brakingforce during this process, an additional vehicle deceleration resultsand part of the impact energy is absorbed by the friction between tiresand roadway so that collision damage is attenuated and in particulardeformation of or damage to the vehicle's relatively rugged passengercompartment is largely avoided. At point in time t4, the collision isterminated, because the obstacle has been tossed away; the speed of thehost vehicle, however, is not yet reduced to zero. Braking command Bcontinues to be active so that the vehicle is slowed down further. Inthis way, an uncontrolled movement of the vehicle after the collision islargely avoided, even when the driver does not or does no longerintervene in the action. In the example shown in FIG. 1, triggeringdevice 26 also acts upon airbag system 18 and threshold values Sa1 andSa2, which apply to triggering emergency braking, are at the same timethe threshold values for triggering the airbag system. Since in view ofthe imminent collision threshold value Sa1 has been reduced, the airbagsare thus ignited earlier so that they deploy their protection effectearlier and protect the occupants more effectively. The continueddeceleration of the vehicle, even after termination of the collision(point in time t4), additionally contributes to attenuate the recoilmovement of the vehicle occupants after impact with the airbag.

FIG. 3 illustrates the case where collision prediction device 24 doesnot detect the risk of collision for whatever reason, e.g., due toblinding of the radar sensor, so that at point in time t2 an impactoccurs without warning. The threshold value has not been reduced in thiscase, but rather has retained the value Sa 2. This threshold value isonly reached at a later point in time t5 and results then in ignition ofthe airbags and the output of braking command B. Triggering emergencybraking a little later makes it still possible to absorb part of theimpact energy and to attenuate the collision damage to a certain extent.

FIG. 4 shows a modified exemplary embodiment in which collision signal Kis a multi-valued signal which indicates a collision probability between0 (collision impossible) and 1 (collision certain). In this case,triggering device 26 is programmed in such a way that it may outputbraking command B also independently from the signal of impact detectionsystem 16, i.e., already prior to the collision occurrence if theimminent collision is all but certain, namely when collision probabilityP reaches a threshold value SC. To avoid erroneous triggering, thisthreshold value is selected to be just below 1 so that cases may alsooccur in which a collision actually takes place without threshold valueSC being reached. In the example shown, starting at point in time t6collision prediction device 24 detects a certain risk of collision andcollision probability P starts to rise according to curve 30. Thethreshold value for acceleration (−a) measured by impact detectionsystem 16 is varied as a function of collision probability P anddecreases starting at starting value Sa2 to the extent that thecollision probability rises as is indicated in FIG. 4 by curve 32.Collision probability P (curve 30) does not reach threshold value SC,and at a point in time t7 the distance to the obstacle has decreased tothe extent that the radar sensor may no longer execute a reliabledistance measurement. Collision probability P may therefore no longer beupdated, but is kept on the value reached which is indicated by a dashedcontinuation of curve 30. Accordingly, the threshold value for theacceleration remains value Sa3. At point in time t8, curve 28 reachesthis threshold value which triggers the output of braking signal B (andpossibly the ignition of the airbags). It is thus ensured that, evenwith insufficiently high collision probability, emergency braking istriggered, at the beginning of the collision at the latest.

The dependence of the threshold value for the acceleration (curve 32) oncollision probability P must be such that emergency braking is notalready triggered when the driver himself activates the brake, therebydecelerating the vehicle. This means that, as long as collisionprobability P remains below threshold value SC, the threshold value forthe acceleration must be greater than the maximally reachable vehicledeceleration.

According to a refinement, the braking force actually exerted on thevehicle brake may be measured and the vehicle deceleration correspondingto this braking force may be subtracted from the acceleration measuredby impact detection system 16 so that curve 28 indicates only thedeceleration caused by the impact. In this case, the threshold valuegiven by curve 32 may be reduced to almost 0 so that a highersensitivity of the impact detection is achieved. This is in principlealso possible in the example embodiment according to FIGS. 2 and 3.

A further modification of the example embodiment according to FIG. 4 isthat the threshold value for the acceleration is not varied constantlyaccording to curve 32, but rather changes only from a higher value Sa2to a lower value Sa3 as soon as collision probability P exceeds a lowerthreshold value SC1 (indicated in FIG. 4 by a dashed line). FIG. 5illustrates this specific embodiment using a flow chart.

In step S1, threshold value Sa for the acceleration is initialized andis set to higher value Sa2. In step S2 it is checked whether (negative)acceleration −a is greater than Sa2. If this is the case, emergencybraking is triggered in step S3 and the airbags are ignited. Otherthreshold values may be applied for igniting the airbags than fortriggering emergency braking.

If the condition checked in step S2 is not met, it is checked in step S4whether collision probability P has reached smaller threshold value SC1.If this not the case the system jumps back to step S1 and theabove-described steps are cyclically repeated in a loop.

If the collision probability exceeds threshold value SC1, thresholdvalue Sa for the acceleration is reduced to Sa 3 in step S5 andtriggering device 26 outputs prefill signal PF. In step S6 it is thenchecked whether the acceleration has reached threshold value Sa 3(beginning of the collision). In this case, emergency braking andignition of the airbags are triggered in step S7. Otherwise, it ischecked in step S8 whether collision probability P has reached higherthreshold value SC. If negative, the system jumps back to S1 andotherwise emergency braking is triggered in step S9.

Subsequent to step S9, it is checked in step S10 whether the anticipatedcollision moment calculated by collision prediction device 24 hasalready been exceeded. If this not the case, it is checked again in stepS11 whether acceleration −a has exceeded threshold value Sa1. Ifpositive, i.e., when the collision begins, the airbags are ignited instep S12. Otherwise, the system jumps back to step S10 and the loopcontaining steps S10 and S12 is repeated until the collision occurs. Ifthe anticipated collision does not occur despite high collisionprobability P (step S8), the loop is abandoned via step S10 andemergency braking is aborted in step S13 in order to prevent a rear-endcollision with a following vehicle.

Steps S2, S3, and S8 through S13 may be omitted in a simplified exampleembodiment.

1. A safety device for a motor vehicle, comprising: an impact detectionsystem configured to measure an acceleration of the vehicle caused by animpact; and a triggering device adapted to trigger a braking operationas a function of a signal of the impact detection system; wherein thetriggering device is configured to trigger the braking operation whenthe impact detection system indicates a beginning of an impact.
 2. Thesafety device according to claim 1, wherein the impact detection systemis part of an airbag system and is also configured to activate anairbag.
 3. A safety device for a motor vehicle, comprising: an impactdetection system; a triggering device adapted to trigger a brakingoperation as a function of a signal of the impact detection system,wherein the triggering device is configured to trigger the brakingoperation when the impact detection system indicates a beginning of animpact; a position-finding system adapted to locate obstacles in frontof the vehicle; and a collision prediction device configured to predictan imminent collision with an obstacle, wherein triggering of thebraking operation by the triggering device is dependent on a result ofthe collision prediction.
 4. The safety device according to claim 3,wherein the impact detection system includes at least one accelerationsensor configured to measure the acceleration of the vehicle caused bythe impact, and the triggering device is configured to trigger thebraking operation when the acceleration exceeds a threshold value and tovary the threshold value as a function of the result of the collisionprediction.
 5. The safety device according to claim 4, wherein theimpact detection system is part of an airbag system and is alsoconfigured to activate an airbag, the triggering device configured tovary the threshold value for triggering the airbag system as a functionof the result of the collision prediction.